This invention relates to a technique for overcoming an evil effect arising from the non-uniformity of illumination light caused by a secular change, individual differences and so forth in an application of an illumination apparatus in which a laser light source is used and an image production apparatus such as a projector or a printer in which an illumination apparatus of the type mentioned is used.
An optical system is known which uses a plurality of laser light sources or a plurality of laser beams to implement illumination of a uniform light intensity distribution. Where an optical system of the type described is applied, for example, to an image display apparatus of the projection type, a linear beam is illuminated on an optical modulation element of the one-dimensional spatial modulation type. The optical modulation element modulates the light to obtain a one-dimensional image. The one-dimensional image is scanned along a direction perpendicular to the one-dimensional direction by a light scanning mechanism such as a galvanometer and projected on a screen to form a two-dimensional image. It is to be noted that, as one of optical modulation elements of the one-dimensional spatial modulation type, for example, a grating light valve device (hereinafter referred to simply as “GLV” (trademark) device) developed by Silicon Light Machines (SLM) (trademark), United States, can be listed. The GLV device is formed from reflection type diffraction gratings, and a plurality of movable ribbons are disposed at predetermined distances while a fixed ribbon is disposed between each adjacent ones of the movable ribbons. When a driving voltage is applied between a common electrode and the movable ribbons, the movable ribbons are moved to form diffraction gratings to incident light.
In illumination on such a one-dimensional optical modulation element as described above, it is necessary for the light intensity to be uniform within a predetermined range (“top hat”-shaped distribution). A design technique for uniformization of the light intensity is disclosed, for example, in Japanese Patent Laid-Open No. 2003-218017 (hereinafter referred to as Patent Document 1). According to the design technique disclosed in Patent Document 1, where a laser array light source and a fly-eye lens are used to achieve uniform illumination, in order to enhance the uniformity of the intensity distribution even where the divisional number of the fly-eye lens is an exact devisor of the laser array number, spatial phases of profiles of laser array light incident to the lens arrays are made different from each other.